The present invention resides in the field of semiconductor devices, and in particular relates to methods for treating semiconductor devices or components thereof in order to reduce the degradation of semiconductor device characteristics over time.
As further background, hydrogen passivation has become a well-known and established practice in the fabrication of semiconductor devices. In the hydrogen passivation process, defects which affect the operation of semiconductor devices are removed. For example, such defects have been described as recombination/generation centers on active components of semiconductor devices. These centers are thought to be caused by dangling bonds which introduce states in the energy gap which remove charged carriers or add unwanted charge carriers in the device, depending in part on the applied bias. While dangling bonds occur primarily at surfaces or interfaces in the device, they also are thought to occur at vacancies, micropores, dislocations, and also to be associated with impurities.
Over the years a number of hydrogen passivation processes have been proposed. For example, U.S. Pat. No. 3,923,559 describes a process in which, in the fabrication of a device such as a metal oxide semiconductor field effect transistor (MOSFET) device, hydrogen gas is introduced into the layer of silicon dioxide prior to deposition of the metal electrodes. Thereafter, the metal electrodes are deposited, thereby trapping the hydrogen gas within the device. Thereafter, the device is annealed at an elevated temperature and the hydrogen previously introduced migrates to the silicon surface to neutralize undesirable interface states produced during device fabrication.
U.S. Pat. No. 4,151,007 describes a passivation process in which the last fabrication step in the device fabrication involves heating the device in an ambient of hydrogen gas at a temperature of 650.degree. C. to 950.degree. C. This final hydrogen anneal step reportedly negated the effects of slow trapping and thus improved the stability of the MOS structures.
U.S. Pat. No. 4,113,514 describes a passivation process which involves exposing the device to atomic hydrogen, for example generated using a glow-discharge apparatus acting upon molecular hydrogen, at a temperature lower than 450.degree. C. Somewhat similarly, U.S. Pat. No. 4,331,486 describes a passivation process in which a hydrogen plasma is created to treat the semiconductor devices with atomic hydrogen.
U.S. Pat. No. 3,849,204 describes a passivation process which involves implanting hydrogen ions in the area of defects, and thereafter annealing the substrate in an inert atmosphere to eliminate the interface states.
Another problem which has arisen in the semiconductor industry is the degradation of device performance by hot carrier effects. This is particularly of concern with respect to smaller devices in which proportionally larger voltages are used. When such high voltages are used, channel carriers can be sufficiently energetic to enter an insulating layer and degrade device behavior. For example, in silicon-based P-channel MOSFETs, channel strength can be reduced by trapped energetic holes in the oxide which lead to a positive oxide charge near the drain. On the other hand, in N-channel MOSFETS, gate-to-drain shorts may be caused by electrons entering the oxide and creating interface traps and oxide wear-out. "Drain engineering" has been an emerging field attempting to cope with these problems, for example involving the use of a lightly-doped drain (LDD) in which a lightly-doped extension of the drain is created between the channel and the drain proper. For additional detail as to these and other potential measures for reducing susceptibility to hot carrier effects, reference can be made for example to U.S. Pat. Nos. 5,352,914, 5,229,311, 5,177,571, 5,098,866, 4,859,620, 4,691,433 and 4,521,698. Such solutions are, however, expensive because they typically complicate the fabrication process. Their avoidance, or at least their simplification, would be desirable.
In light of this background there exists a need for improved passivation processes and devices resulting from such processes. The present invention addresses these needs.